In the consolidation or compacting of poured concrete aggregate, to eliminate voids therein, it is common practice to employ vibration generators which are immersed in the poured aggregate and moved to various positions therein to create local vibrations which cause the aggregate to settle into a voidless mass, essential for maximum strength when the mass sets. Such generators are often formed as elongated prods of relatively small diameter so that they may be immersed between obstructions, such as reinforcing steel, placed in a form prior to pouring the aggregate. Often, the vibration generator is an unbalanced rotor, rotated by a power source, such as an air motor disposed within the prod adjacent one end of the rotor, the air motor being supplied with air under pressure through flexible supply and exhaust hoses connected to one end of the prod. Flexible drive shafts have also been proposed, one end of the flexible shaft being connected to a suitable remote motor. Further, electric motors, contained within the prod, have been proposed.
Of the various motors of small size and relatively high power which may be incorporated in the space available with the prod, piston, vane and spur gear motors all present possibilities but each has its disadvantages. For example, piston motors are usually complicated due to their various movable parts, including valves. Vane motors are usually somewhat more simple but may be subject to considerable wear from foreign matter in the fluid operating medium. Paired conventional meshing gears are simplest of the various motors referred to but the axes of rotation are spaced apart creating a large objectionable enclosing envelope and some sort of transmission mechanism to place the axis of an output drive shaft on the geometric axis of the prod. Theoretically then, a turbine, rotatable about the prod and rotatable weight axis would provide the ideal drive in a minimum space. Turbines, however have poor torque at lower speeds and to obtain a desired output torque it is necessary to rotate the turbine at extremely high speed and reduce it through a speed reducer. It is not uncommon for the speed reducer to be many times larger than the turbine. A turbine, of course, is not a positive displacement motor (or engine) like the others referred to and derives its torque through fluid velocity, either through the principle of impulse or reaction (or a combination thereof).
Where the eccentric weight speed is of the order of 10,000-12,000 RPM this presents problems for driving same directly by an electric motor. While electric motors operating at such speeds on conventional 60 cycle AC are well known, they are of the "universal" type which require commutators and brushes which adds to the complexity of construction and which also require periodic maintenance.
Certain engine driven paving machines are also well known which drive their various instrumentalities mechanically or by a high pressure hydraulic circulating pump. They are, however, devoid of an electrical or air source of energy for operating a vibrator. Also, if the vibrator were driven by a flexible shaft, as is well known, this would require a cumbersome engine power take-off and speed change transmission to operate the vibrator at optimum speed. It becomes apparent, accordingly, and particularly for use with a paving machine of the type referred to, that improvements in a vibrator drive means would be advantageous to meet the various criteria involved in an optimum manner of simplification.